1. Field of the Invention
This invention relates to a fuel composition containing an aliphatic hydrocarbyl-substituted amine or a poly(oxyalkylene)amine and an ester of a carboxylic aid and a polyhydric alcohol. In a further aspect, this invention relates to the use of the present fuel composition in an internal combustion engine to reduce friction and thereby improve fuel economy.
2. Description of the Related Art
There has been considerable effort in recent years to improve the fuel economy of motor vehicles. One approach to reducing fuel consumption has been the development of lubricants and lubricating oil additives which reduce engine friction and thus reduce energy requirements. However, the improvements in fuel efficiency obtained with lubricating oil friction reducing additives have been modest and are typically difficult to ascertain without statistical testing in a number of internal combustion engines. Accordingly, increasing effort is now being spent in developing fuel additives as friction modifiers to provide greater fuel economy by reducing friction in the combustion chamber of an internal combustion engine.
Since the conditions in an internal combustion chamber are substantially different from, and much more severe than, those in a crankcase, the fact that a particular additive or class of additives has benefited the performance of a lubricating oil in an internal combustion engine does not mean that benefits will be gained by using the same types of compounds as additives in the fuel. Accordingly, there exists a need in the art for additional methods to improve the fuel economy of internal combustion engines used to power automotive vehicles.
U.S. Pat. No. 4,617,026 to Shaub et al. discloses a method of reducing fuel consumption in an automotive internal combustion engine which comprises operating the engine with a gasoline fuel containing an additive which is a hydroxyl-containing ester of a monocarboxylic acid and a glycol or trihydric alcohol, wherein the ester additive has at least one free hydroxyl group.
U.S. Pat. No. 4,609,376 to Craig et al. discloses the use of an additive in alkanol fuels to reduce engine wear and improve lubricity, wherein the additive comprises an ester of a monocarboxylic or polycarboxylic acid and a polyhydric alcohol, and further wherein the ester contains at least two free hydroxyl groups.
U.S. Pat. No. 5,632,785 to Culotta discloses a method for reducing fuel consumption in an internal combustion engine which comprises operating the engine with a fuel composition containing an additive which is an ester of polyhydric polyether having ether oxygens and free and esterified hydroxyl groups in the polyhydric polyether backbone of the ester. This patent further teaches that a specific example of such additives is decaglycerol tetraoleate, which is an ester of decaglycerol and oleic acid containing an average of four adducted oleic acid units and ten to twelve free hydroxyl groups.
In the diesel fuel area, the increased use of diesel fuels having a low sulfur content has led to the development of diesel fuel additives which will improve the anti-wear and lubricity properties of such low-sulfur fuels.
For example, PCT Publication No. WO 96/18706 discloses a diesel fuel composition having a sulfur content of at most 0.2% by weight which contains a minor proportion of a lubricity enhancer, such as the ester of a polyhydric alcohol, in combination with at least one nitrogen compound having one or more substituents of the formula &gt;NR, wherein R is a hydrocarbyl group of 8 to 40 carbon atoms. This publication further discloses that the nitrogen compound may be an amine salt and/or amide formed by reacting at least one molar proportion of a hydrocarbyl-substituted amine and a molar proportion of a hydrocarbyl acid having from 1 to 4 carboxylic acid groups or its anhydride.
PCT Publication No. WO 96/23855 discloses a diesel fuel composition containing not more than 0.05% by weight of sulfur and a minor amount of an additive composition comprising (a) an ashless dispersant comprising an acylated nitrogen compound, and (b) a carboxylic acid or an ester of the carboxylic acid and an alcohol wherein the acid has from 2 to 50 carbon atoms and the alcohol has one or more carbon atoms.
PCT Publication No. WO 96/18708 discloses a diesel fuel composition having a sulfur content of at most 0.2% by weight which contains minor proportions of a lubricity enhancer, such as the ester of a polyhydric alcohol and a carboxylic acid, and at least one ethylene-unsaturated ester copolymer.
PCT Publication No. WO 94/17160 discloses a diesel fuel composition having a sulfur concentration of 0.2% by weight or less and a minor proportion of an additive comprising an ester of a carboxylic acid and an alcohol, wherein the acid has from 2 to 50 carbon atoms and the alcohol has one or more carbon atoms.
In addition, European Patent Application Publication No. EP 0,780,460 A1, published Jun. 25, 1997, discloses a gasoline additive concentrate comprising a lubricity additive selected from the group consisting of saturated and unsaturated fatty acids, oligomerized saturated and unsaturated fatty acids, esters of such fatty acids and oligomerized fatty acids and mixtures thereof, in an aromatic solvent, and containing a compatibilizer which remains liquid at temperatures at least as low as 0.degree. C. selected from the group consisting of an alcohol, an amine, and mixtures thereof. This publication further teaches that the alcohol is a C.sub.2 to C.sub.10 alcohol, preferably a C.sub.2 to C.sub.8 alcohol, and the amine is a C.sub.12 to C.sub.75 amine having at least one nitrogen, preferably a C.sub.12 to C.sub.18 amine.